1. Field of the Invention
The present invention relates to a fingerprint matching processor which has a semiconductor sensor for reading out fingerprint information through the difference in electrostatic capacities and executes a fingerprint information matching process, and more particularly, to a fingerprint matching processor capable of preventing illegal fingerprint matching.
2. Description of the Related Art
A fingerprint matching processor that is configured to read out fingerprint information by means of a fingerprint sensor and check the read out fingerprint information for user identification has been known.
In such a fingerprint matching processor, fingerprint matching using illegally obtained fingerprint information is often conducted. For example, when the fingerprint matching process is performed with a finger placed on a sensor surface of the fingerprint matching processor, dirt, such, as oil on the finger adheres to the sensor surface after the process. This dirt may be used for illegal fingerprint matching.
To prevent such an irregularity, the fingerprint matching processor is configured to determine whether the finger is placed on the sensor surface at the time of the fingerprint matching process and to execute the fingerprint matching process depending on the determination result.
More specifically, when it cannot be determined with certainty whether the finger has come in contact with the sensor surface during a reading operation of fingerprint information, the fingerprint matching processor repeats the reading operation to detect a change in the read out fingerprint information, thereby determining whether the finger has been placed on the sensor surface.
As described above, in the fingerprint matching processor, the matching process of the fingerprint information read out by means of a fingerprint sensor is not started until the placement of the finger on the sensor surface has been determined. As is known, the fingerprint information differs between individuals. Therefore, by employing the method in which the fingerprint matching process is stated after confirmation of placement of the finger on the sensor surface, it can be determined that the fingerprint information read out by means of the sensor is the information inherent to the living organism (human), which makes it possible to identify the individual uniquely.
Further, some fingerprint matching processors have been designed to have a living organism detection means for the determination of the placement of the finger on the sensor surface (refer to Jpn. Pat. Publication No. 3-38621).
However, the above method of determining whether the finger has been placed on the sensor surface by detecting a change in the fingerprint information depends on the condition of the finger or the like. Accordingly, it may be said that this method lacks validity and is an extremely unstable determination method.
Further, in the method using the living organism detection means for the determination of the placement of the finger on the sensor surface, the living organism detection means itself causes the fingerprint matching processor to grow in size and leads to increased cost.